// streams/OptionalFilter.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

import java.util.Arrays;
import java.util.function.Predicate;
import java.util.stream.Stream;

class OptionalFilter {
    static String[] elements = {
            "Foo", "", "Bar", "Baz", "Bingo"
    };

    static Stream<String> testStream() {
        return Arrays.stream(elements);
    }

    static void
    test(String descr, Predicate<String> pred) {
        System.out.println(" ---( " + descr + " )---");
        for (int i = 0; i <= elements.length; i++) {
            System.out.println(
                    testStream()
                            .skip(i)
                            .findFirst()
                            .filter(pred));
        }
    }

    public static void main(String[] args) {
        test("true", str -> true);
        test("false", str -> false);
        test("str != \"\"", str -> str != "");
        test("str.length() == 3", str -> str.length() == 3);
        test("startsWith(\"B\")",
                str -> str.startsWith("B"));
    }
}
/* Output:
 ---( true )---
Optional[Foo]
Optional[]
Optional[Bar]
Optional[Baz]
Optional[Bingo]
Optional.empty
 ---( false )---
Optional.empty
Optional.empty
Optional.empty
Optional.empty
Optional.empty
Optional.empty
 ---( str != "" )---
Optional[Foo]
Optional.empty
Optional[Bar]
Optional[Baz]
Optional[Bingo]
Optional.empty
 ---( str.length() == 3 )---
Optional[Foo]
Optional.empty
Optional[Bar]
Optional[Baz]
Optional.empty
Optional.empty
 ---( startsWith("B") )---
Optional.empty
Optional.empty
Optional[Bar]
Optional[Baz]
Optional[Bingo]
Optional.empty
*/
